Functional Analysis of Environmental DNA-Derived Microviridins Provides New Insights into the Diversity of the Tricyclic Peptide Family

Abstract

bMicroviridins represent a unique family of ribosomally synthesized cage-like depsipeptides from cyanobacteria with potent protease-inhibitory activities. The natural diversity of these peptides is largely unexplored. Here, we describe two methodologies that were developed to functionally characterize cryptic microviridin gene clusters from metagenomic DNA. Environmental samples were collected and enriched from cyanobacterial freshwater blooms of different geographical origins containing predominantly Microcystis sp. Microviridins were produced either directly from fosmid clones or after insertion of environmental DNA-derived gene cassettes into a minimal expression platform in Escherichia coli. Three novel microviridin variants were isolated and tested against different serine-type proteases. The comparison of the bioactivity profiles of the new congeners allows deduction of further structure-function relationships for microviridins. Moreover, this study provides new insights into microviridin processing and gene cluster organization.

Natural Product Biosynthetic Diversity and Comparative Genomics of the Cyanobacteria

“…The cyanobactin pathway was engineered to produce eptidemnamide, a cyclic peptide similar to an anticoagulant in clinical use [73]. New microviridin variants were produced using metagenomic libraries, thereby omitting laborious isolation and cultivation steps for the cyanobacteria [74].…”

Exploration of the Biosynthetic Potential of the Populus Microbiome

“…While microviridins have thus far been isolated only from Cyanobacteria, the in vitro reconstitution of the pathway has enabled the study of microviridins from other bacteria (53,54). Homology searching of the MdnC ATP-grasp ligase in the NCBI database showed that the microviridin biosynthetic machinery is not confined to cyanobacteria but is also present in Proteobacteria and Bacteroidetes, in particular Chryseobacterium (55,56). In vitro experimentation has revealed that microviridins act as protease inhibitors (54), but the natural function in the microbiome of Populus remains to be determined.…”

Mining the Metabiome: Identifying Novel Natural Products from Microbial Communities

“…This includes the tryptophan dimer-based cytotoxins borregomycin and erdasporine (Chang and Brady, 2013; Chang et al, 2013); congeners of a potent antitumor compound pederin (Zimmermann et al, 2009); the pharmacologically important antitumor polyketide psymberin (Fisch et al, 2009); arimetamycin A (9) , a natural doxorubicin analog, that is active against multidrug resistant cancer cell lines (Kang and Brady, 2013); a number of variants of the highly selective protease inhibitor microviridin (Gatte-Picchi et al, 2014; Ziemert et al, 2010) and structurally diverse aromatic polyketides including the MRSA active, tetarimycin A (10) as well as the MRSA and VRE active fasamycins A and B (Feng et al, 2012; Kallifidas et al, 2012); and a penatacyclic compound erdacin, with a novel ring system (King et al, 2009). …”